Official Google Webmaster Central Blog: A proposal for making AJAX crawlable

Webmaster Central Blog

Official news on crawling and indexing sites for the Google index

A proposal for making AJAX crawlable

Wednesday, October 07, 2009

Minimal changes are required as the website grows

Users and search engines see the same content (no cloaking)

Search engines can send users directly to the AJAX URL (not to a static copy)

Site owners have a way of verifying that their AJAX website is rendered correctly and thus that the crawler has access to all the content

Slightly modify the URL fragments for stateful AJAX pages
Stateful AJAX pages display the same content whenever accessed directly. These are pages that could be referred to in search results. Instead of a URL like http://example.com/page?query#state we would like to propose adding a token to make it possible to recognize these URLs: http://example.com/page?query#[FRAGMENTTOKEN]state . Based on a review of current URLs on the web, we propose using "!" (an exclamation point) as the token for this. The proposed URL that could be shown in search results would then be: http://example.com/page?query#!state.

Use a headless browser that outputs an HTML snapshot on your web server
The headless browser is used to access the AJAX page and generates HTML code based on the final state in the browser. Only specially tagged URLs are passed to the headless browser for processing. By doing this on the server side, the website owner is in control of the HTML code that is generated and can easily verify that all JavaScript is executed correctly. An example of such a browser is HtmlUnit, an open-sourced "GUI-less browser for Java programs.

Allow search engine crawlers to access these URLs by escaping the state
As URL fragments are never sent with requests to servers, it's necessary to slightly modify the URL used to access the page. At the same time, this tells the server to use the headless browser to generate HTML code instead of returning a page with JavaScript. Other, existing URLs - such as those used by the user - would be processed normally, bypassing the headless browser. We propose escaping the state information and adding it to the query parameters with a token. Using the previous example, one such URL would be http://example.com/page?query&[QUERYTOKEN]=state . Based on our analysis of current URLs on the web, we propose using "_escaped_fragment_" as the token. The proposed URL would then become http://example.com/page?query&_escaped_fragment_=state .

Show the original URL to users in the search results
To improve the user experience, it makes sense to refer users directly to the AJAX-based pages. This can be achieved by showing the original URL (such as http://example.com/page?query#!state from our example above) in the search results. Search engines can check that the indexable text returned to Googlebot is the same or a subset of the text that is returned to users.

http://example.com/dictionary.html#AJAXhttp://example.com/dictionary.html#!AJAXhttp://example.com/dictionary.html?_escaped_fragment_=AJAXhttp://example.com/dictionary.html#!AJAXView the presentationWebmaster Help ForumProposal by Katharina Probst, Bruce Johnson, Arup Mukherjee, Erik van der Poel and Li Xiao, Google
Blog post by John Mueller, Webmaster Trends Analyst, Google Zürich